1. The Field of the Invention
This invention relates to equipment for trucks and, more particularly, to novel systems and methods for providing adjustable axles for trucks.
2. The Background Art
Highway construction and maintenance is a matter of substantial concern to local, state, and federal governments. Road construction has always been an expensive proposition. Roads constructed using modern knowledge, methods, and technology have greatly improved the load-bearing capacity of vehicles traveling over those roads.
Specific limitations exist on loading of vehicle axles. It is well established that bridges are designed to carry specific weights. However, in actual bridge design, several additional, localized factors exist. For example, bridges may have one or more surfacing materials, such as concrete or asphalt. The surfacing materials may be designed in various compositions to support various loads and provide predictable durability. However, underlying a bridge or road surface is a structure of specific members each designed for supporting a particular maximum force or load.
Bridges in various parts of a roadway system have varying weight-carrying capacities. A truck having weight over some number of axles, must also have those axles distributed across a suitable length of the bridge in order to distribute the load of the truck properly over the individual structural members of the bridge.
Thinking in terms of a truck, not as a truck, but as a series of axles, each bearing a load, one sees another important factor in the mutual design criteria between vehicles and roadways (e.g. bridges). That is, axles cannot be separated from the truck. The truck has a length; therefore, axles cannot be completely separated from each other. Therefore, all of the axles of the truck will pass over the bridge together. The truck has to distribute axles over some maximum length.
Moreover, the construction of all bridges, streets, highways and roads provides for specific limitations on sustainable loads and the like. For example, just as building construction must start far below the surface level of the earth to support a foundation, many road beds must be deeply laid to provide acceptable sustainable loads. Above a road bed are laid various types and grades of materials. Ultimately, a surface material is provided on which vehicles roll directly.
Pneumatic tires, in addition to improving a vehicle""s ability to absorb shocks from the roughness of a surface, distribute the load of the vehicle over a surface area of a road surfacing material. Tire pressures relate directly to the distortion of a tire in order to present a certain amount of area onto a road for supporting the weight of the vehicle. For example, a four thousand pound vehicle having a total of fifty square inches of tire surface to the road must have a tire pressure of approximately twenty pounds per square inch to support the load. To support the same load or weight of a vehicle at forty pounds per square inch only twenty-five square inches of tire tread must be in contact with the road. Thus, local pressure on a road surface may be controlled, to a certain extent, by the inherit limits on tire pressures.
The distance between a vehicle""s axles is another factor in load distribution on a road bed. For example, two axles spaced relatively closely together will produce more load in a road bed than the same two axles, carrying the same loads, but spaced further apart. Thus, axle location may be very important in determining the local force presented on a bridge or a road bed by a particular axle. In this context, an axle may be used to refer to the axle itself, or to the axle and tires as they represent force application to a road bed from a vehicle supported thereby.
The regulated carrier industry includes many types and classes of trucks. Trucks require both operable hardware and regulatory compliance. Trucks must comply with weight and dimensional limits for roads and especially bridges. Meanwhile, unnecessary wear is avoidable if unused portions, such as unneeded auxiliary axles, of a truck may be disengaged. For example, the basic structure of a truck includes a steering axle and a drive axle mounted to a frame supporting a cab and a bed. Drive wheels may be arranged as duals, tandems, or dual tandems.
In certain circumstances, auxiliary axles may benefit a truck. Auxiliary axles provide load-bearing capacity that may be installed to operate permanently or selectively. Auxiliary axles may be positioned to lead the drive wheels, follow the drive wheels, or trail the entire vehicle. Often the requirement to selectively distribute the load on road beds and bridges drives the positioning of auxiliary axles. Suspension systems may vary depending upon the mounting arrangement of any axle on a truck. Moreover, axles that must be engageable selectively may require their own particular adaptations to meet with the manufacturer""s specifications for the frame of the truck.
Trucks today may be manufactured to have tandem axles spaced a comparatively long distance apart, as compared with trucks of previous years. Also, many trucks now carry auxiliary axles that can be engaged for distributing a load along a different length of the truck. For example, long truck bodies or trailers may have wheels located nearer the front end, rather than leaving the entire weight distributed between a front axle and a rear axle or between a tractor and a pair of closely spaced tandem axles at the rear.
Auxiliary axles are often added to concrete mixer trucks to accommodate limitations on bridge weights. Also, auxiliary axles may be added to accommodate the large differential load between an empty truck and a loaded truck. Thus, auxiliary axles may be engaged for a limited time, only while a vehicle is loaded and is traveling on a road. At a work site, a truck may not need auxiliary axles as a support for the vehicle itself, and may disengage them.
Thus, heavily loaded trucks having changes in load actually applied thereto, may need auxiliary axles. Those axles need to be distributed along a maximum length, and may need to be distributed along the vehicle itself. To protect roadways, to satisfy bridge weight limitations, and to support substantial loads, auxiliary axles may be used in vehicle construction.
Truck manufacturers may regard axles of all types as materials. That is, a truck manufacturer may simply purchase axles from a suitable, available supplier. A truck design may be built to accommodate the particular dimensions of a preferred or suitable axle available from a known manufacturer. Not every truck is, however, custom designed. Often, a manufacturer or purchaser of a truck may desire to install a non-standard axle, such as an auxiliary axle, in order to satisfy a particular need of a particular customer. The customer""s needs may be driven by the task to be performed by the truck and the specific limitations on loading of axles applicable to the geographic region in which the truck will be operated.
Inventory is a perennial problem for manufacturers. If a manufacturer produces a comparatively broad range of designs of trucks, a correspondingly broad range of axle designs may be required. Many designs are sensitive to axle height, as compared to truck frame height. The required suspension system mounting the axle assembly to a truck frame must also be taken into consideration.
Accordingly, it would be an advance in the art to reduce inventories and design commitments by providing both principal and auxiliary axles adaptable to fit a plurality of vehicle heights. Moreover, it would be an advance in the art to provide an axle assembly that could be inventoried for a truck design, the corresponding frame height thereof, and the particular suspension desired, before all decisions concerning the dimensions of the suspension system and the truck frame height have been determined.
Thus, an axle design that provides an adjustable, relative height between the center line of the associated wheels and the mounting surface of the axle with respect to a suspension system, would reduce inventory, reduce cost, and provide design flexibility. Design flexibility can be very important, since the more factors that may be determined at a later time, the more custom performance may be provided. That is, intransigent requirements driven by an inflexible design parameter associated with a particular component of a vehicle may drive costs upward for other features of the vehicle. Moreover, incompatibilities between components require specialized combinations that must be designed, documented, maintained, and so forth in order to support a production line thereof.
In view of the foregoing, it is a primary object of the present invention to provide adjustable height for auxiliary axles, and principal axles of a truck. It is contemplated that an apparatus and method in accordance with the invention may provide any principal axle (steering axle, drive axle) or auxiliary axle (leading axle, following axle, trailing axle) with a suitable range of adjustment for the relative height between the top mounting surface of the axle and the centerline of the associated wheels installed thereon.
Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a method and apparatus are disclosed in one embodiment of the present invention as including an axle structure provided with a bracket for securing a mount thereto. Apertures in the bracket and mount may be positioned to match at a plurality of positions. Thus, fasteners may secure the mount to the bracket on each end of the axle at multiple relative positions therebetween.
A standoff may be provided with the mount, for spacing a wheel assembly a distance away from the end bracket of the axle. Various sizes of tires and wheels may be accommodated by the adjustability between the mount and the bracket of the axle.
The axle may mount to a frame of a vehicle by various mechanisms. A conventional suspension system may secure the axle to the vehicle frame, or a xe2x80x9cpusherxe2x80x9d assembly for selectively engaging the axle may be relied upon. In certain embodiments, a swing arm may mount a trailing axle to a vehicle.
The axle may be formed as a beam of any suitable configuration, including an I-beam, a channel, a box beam, a right circular cylindrical tube, or the like, as a like. Various struts, gussets, fasteners, and the like may secure the brackets to the axle, and the mounts to their respective standoffs for supporting the axle on a vehicle, and the wheels with respect to the axle, respectively. In one embodiment, the mounting hardware for connecting an axle to a vehicle may be integral to the axle. In an alternative embodiment, the axle may be integrally constructed with the suspension system to further reduce weight. Accordingly, the adjustable standoffs for the wheel assemblies may be adjusted to fit the vehicle supported by the apparatus.
Wheel assemblies may be connected to the mount associated with an axle by means of kingpins, axles, drive axles, fixed spindles, or the like. Thus, a wheel assembly may serve as a driver, a steering assembly, or an auxiliary assembly. Also, a wheel assembly may function as a caster on a kingpin connected to a mount and bracket associated with an axle.
In certain embodiments, tie rods may connect wheels that caster or turn, and may connect to dampers (hydraulic or pneumatic buffers) for reducing oscillations.
Universal joints may connect drive axles to axle stubs or spindles driving wheel assemblies. Accordingly, a differential may be provided within an axle in accordance with the invention, having drive axles contain therein for driving connected wheel assemblies. Thus, an axle assembly in accordance with the invention may serve as a principal steering axle of a vehicle, a drive axle of the vehicle, an auxiliary leading or following axle or as a trailing axle, having castered or noncastered wheels mounted thereto.
The standoff assembly may be straight, angled, offset (vertically or horizontally), shimmed (vertically or horizontally), hollow, filled, or the like, in accordance with the desired functionality for the wheel assemblies connected to the axle. Thus, a standoff may position a drive wheel a distance away from a bracket of an axle, both horizontally and vertically, in order to accommodate vehicle size, axle size, suspension dimensions, and any requirement for mobility (e.g. U joints and drive-ins).